Bonding device and method

ABSTRACT

A device and method for bonding objects to be bonded each having a metal bonding portion on a substrate, comprising cleaning means for exposing the metal bonding portions to a plasma having an energy enough to etch the surfaces of the metal bonding portions at a depth of 1.6 nm or more over the entire surfaces of the metal bonding portions under a reduced pressure and bonding means for bonding the metal bonding portions of the objects taken out of the cleaning means in an atmospheric air. By using a specific scheme, metal bonding portions after the plasma cleaning can be bonded in the atmospheric air, thereby significantly simplifying the bonding process and the whole device and lowering the cost.

TECHNICAL FIELD OF THE INVENTION

The present invention relates to bonding device and method for bondingobjects to be bonded each having a metal bonding portion on a surface ofa substrate, such as chips, wafers or various circuit boards.

BACKGROUND ART OF THE INVENTION

As a method for bonding objects to be bonded each having a bondingportion, Japanese Patent 2,791,429 discloses a bonding method of siliconwafers for, at the time of bonding the bonding surfaces of the siliconwafers to each other, sputter etching the bonding surfaces byirradiating an inert gas ion beam or an inert gas high-speed atomic beamto the surfaces at a vacuum condition with a room temperature prior tothe bonding. In this bonding method, oxides or organic substances on thebonding surfaces of the silicon wafers are removed by theabove-described beam and the surfaces are formed by atoms activated bythe beam, and both surfaces are bonded to each other by a strong bondingforce between the activated atoms. Therefore, in this method, basicallyheating for bonding is not necessary, and it is possible to bond theobjects at a room temperature or a low temperature close to the roomtemperature merely by bringing the activated surfaces into contact witheach other.

In this bonding method, however, the bonding of the etched bondingsurfaces must be carried out in a vacuum at a condition where thesurface activated state is maintained. Therefore, the predeterminedvacuum condition must be maintained from the surface cleaning by theabove-described beam to the bonding, and in particular, because at leasta part of the mechanism for bonding must be constructed in a chambercapable of maintaining the predetermined vacuum degree, a large-scalesealing mechanism is required, and the whole of the device becomes largeand expensive. Further, if it is tried to carry out the surface cleaningand the bonding at different places for separating the surface cleaningprocess by the above-described beam and the bonding process from eachother, it is required to maintain a predetermined vacuum conditionbetween both places and mean for conveying the objects from a cleaningplace to a bonding place while maintaining the predetermined vacuumcondition is required, and therefore, it becomes difficult to design apractical device and the whole of the device becomes large.

DISCLOSURE OF THE INVENTION

Accordingly, paying attention to the above-described problems, as theresult of investigation and examination for particularly simplifying thebonding step while ensuring the merit in the bonding due to theabove-described surface activation of the bonding surface as much aspossible, the inventors of the present invention have succeeded to bondthe metal bonding portions of objects to be bonded in an atmosphericair.

Namely, an object of the present invention is to clean metal bondingportions of objects to be bonded by a specific scheme as well as toenable to carry out the bonding after the cleaning in an atmosphericair, and in particular, to simplify the bonding device and the wholedevice and lower the cost.

To accomplish the above object, a bonding device according to thepresent invention for bonding objects to be bonded each having a metalbonding portion on a surface of a substrate, comprises cleaning meansfor exposing the surfaces of the metal bonding portions to a plasmahaving an energy enough to etch the surfaces of the metal bondingportions at a depth of 1.6 nm or more over the entire surfaces of themetal bonding portions under a reduced pressure, and bonding means forbonding the metal bonding portions of the objects taken out of thecleaning means to each other in an atmospheric air.

In this bonding device, it is preferred that the above-described bondingmeans has heating means and bonds the metal bonding portions to eachother at a temperature of 180° C. or lower, preferably, a temperaturelower than 150° C. Although it is preferred that the objects can bebonded at a room temperature without heating, because it is consideredthat, by heating, the atomic movement for bonding is more activated andthe bonding surfaces are more softened to close fine gaps between thebonding surfaces more easily, there is a case where using such a heatingtogether is preferred. However, even if the heating is carried out,because it may be carried out at a temperature of 180° C. or lower,preferably, a temperature lower than 150° C., the load to the device maybe small. Namely, although a typical conventional example for bonding ata low temperature is to use a solder and it has been necessary to heatthe solder at a temperature of 183° C., which is the melting point ofthe solder, or higher, in the present invention, the bonding at atemperature of such a temperature or lower (180° C. or lower,preferably, lower than 150° C.) becomes possible. Especially, in a casewhere the metal bonding portion is gold, bonding at 100° C. or lowerbecomes possible.

Further, in this bonding device, it is preferred that the surfaces ofthe metal bonding portions to be bonded to each other are both formedfrom gold. The whole of electrodes, etc. forming the metal bondingportions may be formed from gold, and only the surfaces thereof may beformed from gold. The formation for forming the surfaces from gold isnot particularly restricted, and the formation of gold plating or a thingold film formed by sputtering or deposition may be employed.

In the bonding device according to the present invention, the cleaningmeans comprises means for irradiating a plasma at an energy capable ofetching the surfaces of the metal bonding portions at a depth of 1.6 nmor more over the entire surfaces of the metal bonding portions to bebonded. By plasma irradiation at such an etching energy or more, itbecomes possible to conduct a surface etching necessary to bond themetal bonding portions to each other in an atmospheric air. Further, asthe cleaning means, an argon plasma irradiating means is suitable, whichcan easily control the plasma intensity and which can a desired plasmaefficiently at a required place.

The above-described bonding means is preferably means for making adispersion of a gap between the metal bonding portions at the time ofbonding to be 4 μm or less at maximum. If the dispersion of the gap is 4μm or less, it becomes possible to suppress the gap within a dispersionof gap required for bonding the metal bonding portions to each other, byan appropriate bonding load.

Further, the above-described bonding means is preferably means formaking a surface roughness of at least one metal bonding portion afterbonding to be 10 nm or less by applying an appropriate bonding load. Ifthe surface roughness is made at 10 nm or less, it becomes to bond at alow temperature, for example, at a room temperature. Further, in orderto achieve such a surface roughness after bonding of 10 nm or less, itis necessary to prevent an excessive surface roughness before bonding,and for example, it is preferred that the surface roughness of at leastone metal bonding portion before bonding is made to be 100 nm or less.

The bonding load is preferably suppressed at a practically adequatevalue or less, for example, in order to prevent bumps from being brokenor from being deformed excessively, particularly, in order to prevent abad affection from being given to a circuit under bumps. Namely, theabove-described bonding means is preferably means for bonding the metalbonding portions to each other at a bonding load of 300 MPa or less.Because generally a stress, which a semiconductor circuit can bear, isconsidered to be 300 MPa, by making the bonding load at 300 MPa or less,the above-described inconvenience can be avoided.

Further, in order to achieve a good close contact between surfaces whenthe metal bonding portions are bonded to each other, it is preferredthat the surface hardness of the metal bonding portions is set at 100 orless in Vickers hardness Hv. For example, the surface hardness Hv ispreferably in a range of 30 to 70 (for example, an average Hv: 50). Byseting the surface at such a low hardness, the surfaces of the metalbonding portions can be appropriately deformed and a closer contactbecomes possible.

Further, in the bonding device according to the present invention, inorder to achieve a desired electric connection over the entire area of apredetermined region of the bonding surfaces, a good parallelism at thetime of bonding becomes an important factor. Therefore, theabove-described bonding means is preferably means capable of adjustingthe parallelism in a bonding area between substrates at the time ofbonding the metal bonding portions to each other at 4 μm or less (4 μmor less as range).

Further, in a case where at least one metal bonding portion is formed bya plurality of bumps, it is preferred that a dispersion of bump heightis 4 μm or less (4 μm or less as range). By this, as aforementioned, itbecomes possible to suppress the dispersion of the gap between the metalbonding portions at the time of bonding at 4 μm or less.

A bonding method according to the present invention for bonding objectsto be bonded each having a metal bonding portion on a surface of asubstrate, comprises the steps of exposing the surfaces of the metalbonding portions to a plasma to etch the surfaces of the metal bondingportions at a depth of 1.6 nm or more over the entire surfaces of themetal bonding portions under a reduced pressure, and bonding the metalbonding portions after the plasma treatment to each other in anatmospheric air.

Also in this bonding method, it is preferred that the metal bondingportions are bonded to each other at a temperature of 180° C. or lower,preferably at a temperature lower than 150° C. Further, a formation canbe employed wherein the metal bonding portions, the surfaces of whichare both formed from gold, are bonded to each other.

Further, in the above-described plasma treatment, in order to carry outa surface etching necessary for bonding the metal bonding portions toeach other in an atmospheric air, the entire surface of the metalbonding portions to be bonded is etched at a depth of 1.6 nm or more. Asthe plasma treatment, an argon plasma treatment can be employed.

Further, it is preferred that the dispersion of the gap between themetal bonding portions at the time of bonding is made to be 4 μm or lessat maximum. Further, it is preferred that the surface roughness of atleast one metal bonding portion after bonding is made to be 10 nm orless. It is preferred that the surface roughness of at least one metalbonding portion before bonding is made to be 100 nm or less.

With respect to bonding load, it is preferred that the metal bondingportions are bonded to each other at a bonding load of 300 MPa or less.Further, it is preferred that the surface hardness of the metal bondingportions is set at 100 or less in Vickers hardness Hv.

Further, it is preferred that the parallelism in a bonding area betweensubstrates at the time of bonding the metal bonding portions to eachother is adjusted at 4 μm or less. In a case where at least one metalbonding portion is formed by a plurality of bumps, it is preferred thatthe dispersion of bump height is 4 μm or less.

The present invention also provides a bonded material made by theabove-described bonding method. Namely, a bonded material according tothe present invention is a bonded material of objects bonded to eachother each having a metal bonding portion on a surface of a substrate,made by exposing the surfaces of the metal bonding portions to a plasmato etch the surfaces of the metal bonding portions at a depth of 1.6 nmor more over the entire surfaces of the metal bonding portions under areduced pressure, and after the plasma treatment, bonding the metalbonding portions to each other in an atmospheric air.

In the above-described bonded material, a structure can be employedwherein at least one object comprises a semiconductor.

In the above-described bonding device and method according to thepresent invention, after the surfaces of the metal bonding portions ofthe objects to be bonded are treated by a plasma so as to be etched at adepth of 1.6 nm or more, the metal bonding portions cleaned andactivated by the etching are bonded to each other in an atmospheric air.Because bonding in an atmospheric air becomes possible, a large-scalevacuum device for bonding and a sealing device therefor are notrequired, the whole of process and the whole of device are simplifiedand the cost can be reduced.

This bonding in an atmospheric air can be achieved in practice, asdescribed later in examples, by suppressing the dispersion of the gapbetween the metal bonding portions at the time of bonding at a smallvalue in addition to the surface cleaning and activation due to theplasma treatment at a predetermined etching energy or more, and further,setting the surface roughness, surface hardness, bonding load, etc. ofthe metal bonding portions, and by combining these conditions.

Thus, in the bonding device and method according to the presentinvention, by appropriately setting various conditions and employing thespecific scheme according to the present invention as described later,it becomes possible to bond the metal bonding portions after plasmacleaning to each other in an atmospheric air, thereby significantlysimplifying the bonding process and the whole device and lowering thecost.

BRIEF EXPLANATION OF THE DRAWINGS

FIG. 1 is a schematic diagram of a bonding device according to anembodiment of the present invention.

FIG. 2 shows a substrate used in an examination as an object to bebonded, FIG. 2A is a plan view of the whole of the substrate, FIG. 2B isan enlarged plan view of a central portion thereof in which many bumpsare formed, and FIG. 2C is an enlarged partial perspective view of thedisposed bumps.

FIG. 3 is a plan view of a chip used in the examination as anotherobject to be bonded.

FIG. 4 is a graph showing a relationship between plasma irradiating timeand connected resistance.

FIG. 5 is a graph showing a relationship between plasma irradiating timeand die shear strength.

FIG. 6 is a graph showing a relationship between bonding load andconnected resistance per one bump.

FIG. 7 is a graph showing a relationship between bonding load and dieshear strength per one bump.

EXPLANATION OF SYMBOLS

-   1: bonding device-   2, 3: metal bonding portion-   4, 5: object to be bonded-   6: vacuum pump-   7: chamber-   8: plasma irradiating means-   9: plasma-   10: Ar gas supplying pump-   11: bonding place-   12: waiting place-   13: turning mechanism-   14: head portion of turning mechanism-   15: bonding head-   16: bonding tool-   17: bonding stage-   18: heater as heating means-   19: cylinder mechanism-   20: vertical guide-   21: lifting device-   22: position adjusting table-   23: two-sight recognition means-   25: bonded material-   31: substrate as object to be bonded-   32: bump-   33: chip as object to be bonded

THE BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, desirable embodiments of the present invention will beexplained referring to figures.

FIG. 1 shows a bonding device 1 according to an embodiment of thepresent invention. An object to be bonded 4 or 5, which has a metalbonding portion 2 or 3 on a surface of a substrate, first, is cleaned ina chamber 7 which is reduced in pressure by a vacuum pump 6 at apredetermined vacuum degree, and the surfaces of metal bonding portions2 and 3 are cleaned by etching by plasma 9 irradiated from plasmairradiating means 8 as cleaning means (cleaning process). In thiscleaning process, metal bonding portions 2 and 3 are plasma treated atan energy capable of etching the entire surfaces of the metal bondingportions 2 and 3 at a depth of 1.6 nm or more. In this embodiment, Argas is supplied into chamber 7 by a pump 10, and the plasma treatment iscarried out under a condition of Ar gas atmosphere and under a conditionof a reduced pressure. Cleaned objects 4 and 5 are taken out of chamber7, and metal bonding portions 2 and 3 are bonded to each other in anatmospheric air at a bonding process (bonding place 11).

Where, the above-described object to be bonded 4 comprises a chip forexample, and the object to be bonded 5 comprises a substrate forexample. Where, the “chip” means all objects with forms being bonded tothe substrate regardless the kind and size, such as an IC chip, asemiconductor chip, an optoelectronic element, a surface mounting part,a wafer a TCP and an FPC. Further, the “substrate” means all objectswith forms being bonded to the chip regardless the kind and size, suchas a resin substrate, a glass substrate, a film substrate, a chip and awafer. As a typical embodiment in the present invention, an embodimentcan be raised wherein at least one object among the objects to be bondedis a semiconductor.

In bonding place 11, for example, the above-described cleaned objects 4and 5 are set at a predetermined waiting place 12. The object 4 is heldby suction, etc. by a head portion 14 of a turning mechanism 13 not totouch the cleaned surface, and after turned over vertically, it is heldby a bonding tool 16 provided at a lower portion of a bonding head 15,by suction, etc., in a form in which the metal bonding portion 2 isdirected downward. The object 5 is held, for example, on a bonding stage17, by suction, etc., in a form in which the metal bonding portion 3 isdirected upward. In this embodiment, a heater 18 is incorporated intobonding tool 16 as heating means, and, in an atmospheric air, bonding ata room temperature and bonding under a heated condition may be bothpossible.

A cylinder mechanism 19 is incorporated into bonding head 15, and apredetermined bonding load can be applied to object 4 held by bondingtool 16 and can be controlled, in a downward direction, namely, in adirection toward object 5. In this embodiment, bonding head 15 can bemoved and positioned in a vertical direction (Z direction) by a liftingdevice 21 (for example, a device having a servomotor and a ball screwmechanism) along a vertical guide 20.

Further, in this embodiment, bonding stage 17 holding theabove-described object 5 can align a position and adjust a parallelismrelative to object 4 by controlling a horizontal position in X and Ydirections, a rotational position in a θ direction and inclinationangles around X and Y axes carried out by a position adjusting table 22provided at a lower position, and the gap between the metal bondingportions at the time of bonding can be suppressed small. These alignmentof the relative position and adjustment of the parallelism are carriedout by reading recognition marks (not shown) provided to objects 4 and 5or the holding means thereof by a recognition means inserted into aposition between the objects 4 and 5 at a condition capable ofprogressing and retreating, for example, a two-sight recognition means23 (for example, a two-sight camera), and performing a necessarycorrection in position and angle based on the read information. Thetwo-sight recognition means 23 can be adjusted in position in X and Ydirections, and as the case may be, in Z direction. Although thesealignment of the relative position and adjustment of the parallelism arecarried out mainly at the side of bonding stage 17 in this embodiment,it is possible to carry out these at the side of bonding head 15 orbonding tool 16, and further, at both sides. In a case carried out atboth sides, according to requirements, it can be also done that, as tothe side of bonding head 15, not only the lifting control but also arotation control and/or a parallelism control may be carried out, andalso as to the side of bonding stage 17, a rotation control, aparallelism control and a lifting control can be carried out, and thesecontrol forms may be arbitrarily combined as needed.

Further, in this embodiment, bonded material 25 formed by bondingobjects 4 and 5 is also put once on waiting place 12, and therefrom, itis conveyed to a next process or a place for stock by an appropriateconveying mechanism (not shown).

EXAMPLES

Using the above-described bonding device, the following examination wascarried out with respect to the bonding method according to the presentinvention. A substrate 31 used in the examination as object to be bonded5 is shown in FIG. 2, FIG. 2A shows a plan view of the whole of thesubstrate 31, FIG. 2B shows an enlarged plan view of a central portionthereof in which many bumps are formed, and FIG. 2C shows an enlargedpartial perspective view of disposed bumps 32, respectively. A chip 33used in the examination as object to be bonded 4 is shown in FIG. 3, andin it, a predetermined circuit pattern is formed corresponding the groupof bumps 32 in the central portion of the substrate.

The specifications of these substrate and chip are as follows.

Substrate: Si substrate, Au plated bumps are formed on an Al pad.

Size of substrate: 20 mm×20 mm

Bump forming region: within 4 mm×4 mm in a central portion

Size of bump: 40 μm×40 μm×height 30 μm (80 μm pitch)

Number of bumps: 400 (refer to FIG. 2B as to bump pattern)

Chip: Au sputter film (Au—0.3 μm/Cr—0.1 μm) on a Si thermally oxidizedsubstrate

Size: 6 mm×6 mm (pattern forming region: within 4 mm×4 mm in a centralportion)

L-type electrode pattern is formed for three terminal determination. (Asthe value of resistance described later, the connected resistance at acorner of the L-type pattern is measured, each side; 10×4)

Under the following conditions, as to the effect for activating thesurfaces of the metal bonding portions due to a short-time plasmairradiation, comparison examinations of bonding in a nitrogen atmosphereand bonding in an atmospheric air after surface cleaning by the plasmatreatment were carried out, and the influence due to the plasmairradiating time in the bonding in each atmosphere was determined as anaverage connected resistance and a die shear strength. As to bonding inan atmospheric air, bonding after leaving for 3.5 minutes and bondingafter leaving for 15 minutes after plasma treatment were examined. Theresults are shown in Tables 1 and 2 and FIGS. 4 and 5.

Conditions of examination for determining the effect due to plasmatreatment:

Plasma deposition electric power: 100 W

Ar flow rate: 30 cc/m

Vacuum degree at the time of introducing Ar: 10 Pa

Vacuum degree at the time of irradiation: 7.5 Pa or less

Bonding load: 20 kgf (50 gf/bump, 300 MPa)

Time for applying load: 1 second

Bonding temperature: 100° C. (373 K)

Maximum value of dispersion of height of electrodes in chip: 2.3 μm

Maximum value of dispersion of height of bumps in Si substrate: 3.0 μmTABLE 1 Variation of die shear strength due to irradiating time (gf)Electric Amount of Irradiating time (sec.) power (W) Atmosphere exposure(min.) 0 3 5 10 30 60 100 atmospheric 3.5 258 — 7058 6595 6008 7406 air100 nitrogen 3.5 252 1035 5587 5896 6507 5427 100 nitrogen 15 — — — 55106373 — 100 atmospheric 15 — — — 5730 5212 — air 50 atmospheric 3.5 2413550 5855 — — — air

TABLE 2 Variation of resistance due to irradiating time (mΩ) AmountElectric of power exposure Irradiating time (sec.) (W) Atmosphere (min.)5 10 30 60 100 atmospheric 3.5 7.28 6.57 6.72 6.90 air 50 atmospheric3.5 6.84 — — — air 100 nitrogen 3.5 6.94 6.4 6.1 6.92 100 nitrogen 15 —6.86 6.70 — 100 atmospheric 15 — 6.40 6.48 — air

As shown in Table 2 and FIG. 4, even in a case of being bonded in anatmospheric air after being left for 15 minutes after plasma treatment,a bonding similar to the bonding in nitrogen was possible, and it wasconfirmed that a sufficiently good bonding could be carried out in anatmospheric air. Further, as shown in Table 1 and FIG. 5, it wasconfirmed that a time of about 5 seconds or more was enough as the timeof the plasma irradiation.

Further, as the result of investigating the relationship between theplasma irradiation and the depth of etching on the surface of the Auplated bump as the surface to be bonded, the depth was about 20 nm/min.in a case of a plasma deposition electric power of 50 W, and the depthwas about 30 nm/min. in a case of a plasma deposition electric power of100 W. In any deposition electric power, as described above, bonding inan atmospheric air was possible by a time of the plasma irradiation ofabout 5 seconds or more. Therefore, it was confirmed that 1.6 nm (=20nm×[5 seconds/60 seconds]) or more was enough as the etching depth forenabling the bonding in an atmospheric air.

Further, Tables 3 and 4 and FIGS. 6 and 7 show the relationships betweenthe bonding load per one bump and the obtained connected resistance ordie shear strength using a bonding temperature as the parameter. Theconditions for the examination are as follows.

Bonding in an atmospheric air

Time for applying load: 1 second

Plasma deposition electric power: 100 W

Irradiating time: 30 seconds

Leaving (exposure) time after irradiation: 3.5 minutes

Other conditions are the same as those aforementioned. TABLE 3 Variationof resistance due to load (mΩ) Load (kgf) Temperature 10 20 30 300 K(27° C.) — 7.28 6.28 373 K (100° C.) 9.55 6.72 5.58 423 K (150° C.) 9.656.47 5.15

TABLE 4 Variation of die shear strength due to load (gf) Load (kgf)Temperature 10 20 30 300 K (27° C.) 3151 5626 5984 373 K (100° C.) 36566595 6406 423 K (150° C.) 4626 6366 8406

It was confirmed that, even if the bonding load per one bump was 50 gfor less, it was possible to obtain a sufficiently practical connectionstate at a low resistance, the die shear strength was enough, and it waspossible to obtain a sufficiently practical connection state even at atemperature of 100° C. (373 K) or lower, or even at a temperature near aroom temperature (27° C., 300 K).

Further, Table 5 shows the relationship between the bonding load per onebump and the surface roughness of the bump after bonding. Because thissurface roughness of the bump after bonding is hard to be determined ifactually bonded, it is determined simulatively by applying a bondingload without plasma irradiation and measuring the surface roughness ofthe bump surface after being deformed by pressing due to the bondingload. It is considered that a bump surface roughness after bonding of 10nm or less is preferable in order to obtain a connection state at asufficiently low resistance. To achieve this, from Table 5, it isunderstood that applying of a load of about 20 kgf is enough and a lowerload is possible, and this value corresponds to a bonding load per onebump of 50 gf. Therefore, it is understood that it is possible toachieve the bump surface roughness after bonding of 10 nm or less evenby a bonding load per one bump of 50 gf or less. Namely, it is possibleeven by a bonding load of 300 MPa or less. However, in order to achievesuch a bump surface roughness of 10 nm or less after pressing, a bumpsurface roughness before bonding is preferably 100 nm or less. TABLE 5Variation of surface roughness of bump (nm) Load (kgf) Temperature 0 510 20 30 300 K (27° C.) — 137 82 6 5 373 K (100° C.) — 145 76 5 4

By the above-described examination, it was confirmed that, in thepresent invention, the bonding in an atmospheric air was possible afterplasma irradiation by setting various conditions appropriately.

INDUSTRIAL APPLICATIONS OF THE INVENTION

The bonding device and method according to the present invention can beapplied to any bonding of objects to be bonded each having a metalbonding portion, and in particular, the bonding device and method aresuitable for bonding in a case where at least one object is asemiconductor.

1. A device for bonding objects to be bonded each having a metal bondingportion on a surface of a substrate, comprising: cleaning means forexposing the surfaces of the metal bonding portions to a plasma havingan energy enough to etch the surfaces of the metal bonding portions at adepth of 1.6 nm or more over the entire surfaces of the metal bondingportions under a reduced pressure; and bonding means for bonding themetal bonding portions of said objects taken out of said cleaning meansto each other in an atmospheric air.
 2. The bonding device according toclaim 1, wherein said bonding means has heating means and bonds themetal bonding portions to each other at a temperature of 180° C. orlower.
 3. The bonding device according to claim 1, wherein the surfacesof the metal bonding portions to be bonded to each other are both formedfrom gold.
 4. The bonding device according to claim 1, wherein saidcleaning means comprises an argon plasma irradiating means.
 5. Thebonding device according to claim 1, wherein said bonding means is meansfor making a dispersion of a gap between the metal bonding portions atthe time of bonding to be 4 μm or less at maximum.
 6. The bonding deviceaccording to claim 1, wherein said bonding means is means for making asurface roughness of at least one metal bonding portion after bonding tobe 10 nm or less.
 7. The bonding device according to claim 1, wherein asurface roughness of at least one metal bonding portion before bondingis made to be 100 nm or less.
 8. The bonding device according to claim1, wherein said bonding means is means for bonding the metal bondingportions to each other at a bonding load of 300 MPa or less.
 9. Thebonding device according to claim 1, wherein a surface hardness of themetal bonding portions is set at 100 or less in Vickers hardness Hv. 10.The bonding device according to claim 1, wherein said bonding means ismeans capable of adjusting a parallelism in a bonding area betweensubstrates at the time of bonding the metal bonding portions to eachother at 4 μm or less.
 11. The bonding device according to claim 1,wherein at least one metal bonding portion is formed by a plurality ofbumps.
 12. The bonding device according to claim 11, wherein adispersion of bump height is 4 μm or less.
 13. A method for bondingobjects to be bonded each having a metal bonding portion on a surface ofa substrate, comprising the steps of: exposing the surfaces of the metalbonding portions to a plasma to etch the surfaces of the metal bondingportions at a depth of 1.6 nm or more over the entire surfaces of themetal bonding portions under a reduced pressure; and bonding the metalbonding portions after said plasma treatment to each other in anatmospheric air.
 14. The bonding method according to claim 13, whereinthe metal bonding portions are bonded to each other at a temperature of180° C. or lower.
 15. The bonding method according to claim 13, whereinthe metal bonding portions, the surfaces of which are both formed fromgold, are bonded to each other.
 16. The bonding method according toclaim 13, wherein an argon plasma treatment is carried out.
 17. Thebonding method according to claim 13, wherein a dispersion of a gapbetween the metal bonding portions at the time of bonding is made to be4 μm or less at maximum.
 18. The bonding method according to claim 13,wherein a surface roughness of at least one metal bonding portion afterbonding is made to be 10 nm or less.
 19. The bonding method according toclaim 13, wherein a surface roughness of at least one metal bondingportion before bonding is made to be 100 nm or less.
 20. The bondingmethod according to claim 13, wherein the metal bonding portions arebonded to each other at a bonding load of 300 MPa or less.
 21. Thebonding method according to claim 13, wherein a surface hardness of themetal bonding portions is set at 100 or less in Vickers hardness Hv. 22.The bonding method according to claim 13, wherein a parallelism in abonding area between substrates at the time of bonding the metal bondingportions to each other is adjusted at 4 μm or less.
 23. The bondingmethod according to claim 13, wherein at least one metal bonding portionis formed by a plurality of bumps.
 24. The bonding method according toclaim 23, wherein a dispersion of bump height is 4 μm or less.
 25. Abonded material of objects bonded to each other each having a metalbonding portion on a surface of a substrate, made by exposing thesurfaces of the metal bonding portions to a plasma to etch the surfacesof the metal bonding portions at a depth of 1.6 nm or more over theentire surfaces of the metal bonding portions under a reduced pressure,and after said plasma treatment, bonding the metal bonding portions toeach other in an atmospheric air.
 26. The bonded material according toclaim 25, wherein at least one object comprises a semiconductor.